This invention relates to a fuel supply control method for internal combustion engines equipped with superchargers, and more particularly to a fuel supply control method of this kind, which is capable of performing a fail-safe function when an abnormality occurs in pressure sensor means for detecting intake pipe pressure which is variable over a wide range during operation of the engine due to the supercharging effect.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by U.S. Pat. No. 3,483,851, which is adapted to determine the valve opening period of a fuel quantity metering or adjusting means for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of at least the intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake air temperature, engine cooling water temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), atmospheric pressure, etc., by electronic computing means.
If such proposed fuel supply control method is applied to an internal combustion engine equipped with a supercharger, in which usually the intake pipe pressure can vary over a wider range than in an internal combustion engine without a supercharger, high detecting accuracy may not be achieved with a single pressure sensor for detecting the intake pipe pressure, to make it impossible to perform accurate control of the fuel quantity being supplied to the engine, thereby badly affecting the driveability, emission characteristics and fuel consumption of the engine.
The term "supercharger", as used through the present specification is defined as a term including not only a turbocharger which is driven by a flow of engine exhaust gases, from an engine, and a supercharger having a compressor coupled to the crankshaft or a camshaft of an engine to be directly driven thereby, but also a type which is driven together with a cooling fan by the crankshaft of an engine via a fan belt and a type which is driven by an electric motor.
In the event that an abnormality occurs in the functioning of pressure sensor means for detecting the intake pipe pressure so that, for instance, fuel is supplied to the engine in a quantity smaller than that actually required by the engine while the engine is operating at a high supercharging rate, the air/fuel mixture supplied to the engine can have a too lean air/fuel ratio. This can not only result in a drop in the engine output, but also badly affect the cooling action of overheated portions of the engine cylinders by fuel contained in the mixture when the engine is in such supercharged operating condition, to cause premature ignition, etc., thereby deteriorating the driveability of the engine, and even to thermally damage the engine parts.